Weighing assembly, coffee grinder and machine comprising same and method for the operation thereof

ABSTRACT

A weighing assembly for weighing an amount of ground coffee with high precision is provided. The weighing assembly includes a container dedicated to ground coffee weighing and weighing means operatively connected to the container. A coffee grinder and a coffee machine, namely a fully automatic coffee machine, are also provided and include the weighing assembly. A method for the operation thereof is also provided.

TECHNICAL FIELD

The present invention relates to a weighing assembly for weighing ground coffee intended to be mounted to or connected to a coffee grinder or to the brewing arrangement of a coffee machine, namely a fully automatic coffee machine.

The present invention also relates to a coffee grinder intended to be mounted to or connected to a coffee machine, namely a fully automatic coffee machine, and including said weighing assembly.

The present invention further relates to a coffee machine, namely a fully automatic coffee machine, comprising said weighing assembly.

The present invention further relates to a method for the operation of said coffee grinder and of said coffee machine.

PRIOR ART

The present invention relates to the technical field of fully automatic coffee machines. Such coffee machines, which work in a fully automatic way and are also called “coffee automats”, allow to start the whole process of the preparation of a coffee-based drink by simply pressing a button and they are widely used in the restaurant industry.

Fully automatic coffee machines are known in which the brewing time of the selected coffee-based drink is measured and the measured brewing time is compared with a brewing time reference value: if the measured brewing time is not within a tolerance range around the brewing time reference value, the coarseness of the coffee powder is varied so as to adjust—through the coffee powder coarseness—the brewing time so that it falls within the predetermined tolerance range.

In order to vary the coffee powder coarseness, the coffee grinder of the coffee machine is provided with stationary blades and movable blades, as well as with means (e.g. servomotors) for moving the movable blades for adjusting their distance from the stationary blades.

These known coffee machines, although they allow a coffee powder coarseness adjustment for obtaining the desired brewing time, nonetheless have some limitations, the most important of which is that they do not take into any account the relationship between coffee powder coarseness and weight of the coffee powder dose used for preparing the selected drink.

The main object of the present invention is to overcome the above-mentioned limitation of prior art by providing a coffee grinder and a corresponding coffee machine allowing to obtain a highly accurate measure of the weight of the coffee powder dose and to take into account the relationship between coffee powder coarseness and coffee powder dose weight.

This and other objects are achieved by the coffee grinder and the coffee machine as claimed in the appended claims.

SUMMARY OF THE INVENTION

According to the invention, a weighing assembly for weighing ground coffee and intended to be mounted to or connected to a coffee grinder or a brewing arrangement of a coffee machine, namely a fully automatic coffee machine, is provided with means for weighing the amount of ground coffee with high accuracy.

To this purpose, the weighing assembly comprises a container dedicated to ground coffee weighing and weighing means operatively connected to said container.

Devices for grinding coffee or similar food which are provided with means for measuring the amount of ground product are known per se in prior art.

By way of example, such a food grinding device is disclosed in U.S. Pat. No. 6,783,089. However, in the food grinding device disclosed in this document, means for measuring the amount of ground product are provided inside the brewing basket. Measuring the amount of ground product inside the brewing basket and together with such basket does not allow for a precise, accurate measure.

On the contrary, due to the fact that the weighing assembly of the invention comprises a container dedicated to ground coffee weighing, the weight of ground coffee can be precisely and accurately measured. According to the invention, a coffee grinder is provided which is intended to be mounted to or connected to a coffee machine, namely a fully automatic coffee machine, and is provided with the weighing assembly of the invention.

The coffee grinder of the invention comprises or is connected to a control device in which a predetermined grinding time for the selected coffee-based drink is stored: when such predetermined grinding time is over, the coffee grinder is stopped and the overall weight of the ground coffee is measured and the corresponding value is sent to said control device.

The ground coffee is then transferred to the brewing arrangement of the coffee machine to which said coffee grinder is mounted or connected.

According to the invention, a method for the operation of the above-disclosed coffee grinder is further provided.

According to the method of the invention, the measured value of the weight of the coffee that was ground during the predetermined grinding time is compared with a reference value of desired weight of the ground coffee dose.

If the measured value does not fall within a tolerance range around the reference value, a new grinding time will be calculated by the control device for the successive grinding cycles.

The invention further relates to a coffee machine comprising the above-disclosed weighing assembly, as well as to a method for the operation thereof.

In the coffee machine of the invention the weighing assembly can be mounted to or connected to the coffee grinder of the coffee machine or the brewing arrangement of the coffee machine itself.

According to the method for operating the coffee machine of the invention, for each selection of a coffee-based drink, the grinding coarseness of the coffee powder and the grinding time, corresponding to a desired brewing time and to a desired weight of the ground coffee dose, respectively, are set.

The brewing time and the weight of the ground coffee dose are measured and compared with the desired reference values: if the measured brewing time does not fall within a tolerance range around the reference value, a new value of coffee powder coarseness will be set for the successive cycles; if the measured weight of the coffee dose does not fall within a tolerance range around the reference value, a new value of grinding time will be set for the successive grinding cycles.

In case, the new values for the powder coffee coarseness and/or the grinding time are calculated by means of respective algorithms of the control device.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will become clearer from the following detailed description of some preferred embodiments of the invention, given by way of example with reference to the attached drawings, wherein:

FIG. 1 is a side view of a weighing assembly according to a first embodiment of the invention;

FIG. 2 is a front view of the weighing assembly of FIG. 1;

FIG. 3 is a side view of a weighing assembly according to a second embodiment of the invention;

FIG. 4 is a front view of the weighing assembly of FIG. 3;

FIG. 5 is a block diagram showing the main steps of the method for the operation of a coffee grinder according to the invention;

FIG. 6 is a schematic view showing the main components of a coffee machine comprising a weighing assembly according to the invention;

FIG. 7 is a block diagram showing the main steps of the method for the operation of the coffee machine comprising a weighing assembly according to the invention.

DESCRIPTION OF SOME PREFERRED EMBODIMENTS OF THE INVENTION

With reference to FIGS. 1 and 2, a weighing assembly, indicated as a whole by reference number 1, for weighing the ground coffee and intended to be mounted to or connected to a coffee grinder or to the brewing arrangement of a coffee machine, namely a fully automatic coffee machine, is shown.

The weighing assembly 1 comprises a container 3 dedicated to the weighing of ground coffee and arranged to receive the coffee powder to be weighed.

The container 3 is mounted on a support 5, which in turn lies on a weighing cell 7 or is otherwise operatively connected thereto.

The weighing cell 7 is provided with its own support 9 for being mounted to or connected to a stationary supporting structure, such as the structure of a coffee machine.

The weighing cell 7 allows to precisely measure the weight of the ground coffee coming from the grinding machine of the coffee grinder, net of the weight of the container 3 and its support 5.

In this respect it is to be noted that, due to the fact that the weighing assembly comprises a container dedicated to the ground coffee weighing, the weight of said container and of its support can be easily determined with high precision and—accordingly—the weight of the ground coffee contained in the container 3 can be easily determined as well.

The weighing assembly 1 is further equipped with a transmitter for transmitting the measured weight of ground coffee to an external device, such as a control device.

The present invention also relates to a coffee grinder intended to be mounted to or connected to a coffee machine, namely a fully automatic coffee machine, and including the weighing assembly 1.

In a per se known manner, said coffee grinder comprises a housing in which a hopper containing coffee beans and a grinding chamber into which the coffee beans contained in said hopper can be transferred, e.g. by gravity, are received; one or more grinding members—preferably driven by a motor, such as an electric motor—cooperating for grinding the coffee beans coming from the hopper and for obtaining a coffee powder are provided in said grinding chamber; the grinding chamber further comprises an outlet spout for discharging the ground coffee powder.

As these element are known per se, they are neither illustrated nor disclosed in greater detail.

The coffee grinder further comprises a weighing assembly 1 according to the invention, which is arranged to receive the coffee powder discharged from the grinding chamber of the coffee grinder.

The coffee grinder of the invention is provided with or connected to a control device (not shown): the coffee grinder receives as an input from said control device a signal for starting the grinding operation as well as a predetermined grinding time, so that the grinding members in the grinding chamber are activated by said starting signal and stop after said predetermined grinding time; on the other hand, the coffee grinder—or more precisely, the weighing assembly 1 of the coffee grinder—sends to said control device the measured value of the ground coffee weight at the end of said predetermined grinding time.

At the end of said predetermined grinding time, once the grinding members of the grinding chamber have been stopped, the ground coffee in the container 3 is taken out thereof.

To this purpose, the container 3 has an outlet port 11 which is closed by a movable panel 13, which normally is in the closed position (e.g. it is kept in the closed position by gravity or by the elastic force of a spring).

At the end of the predetermined grinding time, the movable panel 13 is moved to the open position in order to allow discharging of the ground coffee from the container 3.

To this purpose, the weighing assembly 1 can comprise a magnet 15 and an articulated arm 17 connecting said magnet 15 to said movable panel 13: when the magnet 15 is de-energized, the movable panel 13 is in the normal, closed position; when—at the end of the predetermined grinding time—the magnet 15 is energized, the movable panel 13, through the articulated arm 17, is moved to the open position and the ground coffee is discharged from the container 3.

More particularly, the ground coffee can be discharged in a duct 19 for being transferred to the brewing arrangement of the coffee machine to which the coffee grinder of the invention is mounted or connected.

In FIGS. 3 and 4, a weighing assembly according to an alternative embodiment of the invention is shown, which weighing assembly is indicated as a whole by reference number 1′.

The weighing assembly 1′ comprises a container 3′ dedicated to the weighing of ground coffee and arranged to receive the coffee powder to be weighed.

In this embodiment, the container 3′ is hanging from a support 5′, which in turn is hanging from a weighing cell 7′, which is anchored to a stationary structure by means of its own support 9′.

The bottom of the container 3′ is closed by a movable panel 13′, which under normal conditions is kept in a closed position by the elastic force of a spring 21′.

At the end of the predetermined grinding time, the movable panel 13′ is moved to the open position by energizing a magnet 15′ which is connected to the movable panel through an articulated arm 17′ and overcoming the elastic resistance of the spring 21′, so as to allow discharging of the ground coffee from the container 3′ into a duct 19′ for transferring such ground coffee to the brewing arrangement of a coffee machine.

The alternative embodiment of FIGS. 3—4 has the advantage of providing a container 3′ which is hanging and free from contact with other components of the coffee grinder and/or of the coffee machine, which allows to obtain an even more accurate measure.

With reference to the block diagram of FIG. 5, the operation of a coffee grinder including a weighing assembly according to the invention is substantially as follows:

-   -   upon selection of a given coffee-based drink by the user, the         control device selects the corresponding value of grinding time         stored therein and sends a corresponding value to the coffee         grinder;     -   upon reception of this signal, the coffee grinder is started and         the grinding members of the grinding chamber are activated for         grinding coffee, the ground coffee being transferred from the         grinding chamber to the container 3, 3′ of the weighing assembly         1, 1′;     -   when the selected grinding time has lapsed, the grinding members         of the coffee grinder are stopped and the magnet 15, 15′ is         energized for discharging the ground coffee from the container         3, 3′ into the duct 19, 19′;     -   the measured value of the ground coffee weight obtained by the         weighing cell 7, 7′ before discharging ground coffee from the         container 3, 3′ is sent to the control device and there it is         compared with a reference value corresponding to the selected         coffee-based drink and stored in said control device; if the         value measured by the weighing cell 7, 7′ is equal to the stored         reference value or falls within a tolerance range around said         reference value, no further action is taken; on the contrary, if         the value measured by the weighing cell 7, 7′ does not fall         within said tolerance range, the control device—by means of an         algorithm contained therein—calculates a new grinding time         suitable for obtaining the desired weight of the coffee dose for         the selected drink and replaces the stored grinding time value         by this new value calculated through said algorithm.

Therefore, according to the method of the invention, even if the weight of the coffee dose obtained by the coffee grinder is not consistent with the reference value, no adjustment to the coffee grinder itself is carried out. On the contrary, a different grinding time is set for the successive grinding cycles (for the same drink); this means that the new value of the grinding time is sent to the coffee grinder when the current grinding cycle is already finished and the coffee grinder is ready for the next grinding cycle.

In order to determine the acceptable tolerance range around the reference value of the ground coffee weight, at the beginning of the coffee grinder operation a certain number of measured values (samples) are stored in the control device and checked for determining the aforesaid tolerance range.

With reference now to FIG. 6, the main functional components of a coffee machine 101 comprising a weighing assembly according to the invention are schematically shown.

The coffee machine 101 is a fully automatic machine for preparing espresso and/or other coffee-based drinks, i.e. the whole process for preparing the coffee-based drink is started and carried out upon selection of the desired drink by a user (e.g. by pressing a corresponding button or by acting on a “touch screen” display), without any intervention by an operator.

In general, the coffee machine 101 comprises a brewing arrangement 111 and a dispensing arrangement 131.

More in detail, the coffee machine 101 comprises a brewing arrangement 111 comprising a water pump 113 provided with a flowmeter 115, a boiler 117, and a brewing chamber 121, a valve 119 being provided between the boiler 117 and the brewing chamber 121: in the brewing chamber 121 the water flows through the coffee powder thus preparing the coffee-based drink. The coffee machine 101 further comprises a dispensing arrangement 131, receiving the prepared drink from the brewing arrangement and delivering it to the user through dispensing outlets 133. The delivering arrangement is preferably provided with sensors 135 (e.g. a temperature sensor) in order to detect the properties of the drink prepared by the brewing arrangement 111 and delivered to the user.

In FIG. 6, a coffee grinder 201 is also schematically shown. The coffee grinder 201 comprises a housing 203 in which the grinding chamber is received. One or more grinding members are provided in the grinding chamber: preferably, such grinding members are provided with adjusting means 205 (e.g. servomotors) for varying the distance between the elements of said grinding member so as to obtain coffee powder with different coarseness.

The coffee grinder 201 is operatively connected to the brewing arrangement 111 of the coffee machine 101 so that the ground coffee discharged from said coffee grinder 201 is transferred to the brewing chamber 121 of said brewing arrangement 111 of said coffee machine.

According to the invention, the ground coffee transferred from the coffee grinder 201 to the brewing chamber 121 is weighed by means of a weighing assembly 1 according to the invention.

To this purpose a weighing assembly 1 is interposed between the outlet spout 207 of the coffee grinder 201 and the brewing arrangement 111 of the coffee machine.

According to a first possible embodiment, the weighing assembly is mounted on or connected to the coffee grinder 201.

According to a second possible embodiment, the weighing assembly is mounted on or connected to the brewing arrangement 111 of the coffee machine 101.

Although only a coffee grinder 201 is shown in FIG. 6, the coffee machine 101 could also be provided with several coffee grinders, each of which handles the preparation of the coffee powder for a different coffee-based drink.

The control device(s) controlling the coffee grinder(s) can be the control device of the coffee machine, i.e. the operation of the coffee grinder(s) and of the other components of the coffee machine are controlled by a single, common control apparatus.

As an alternative, the coffee grinder(s) can have its (their) own separate control device(s); in this case, said control device(s) is (are) connected to the control device of the coffee machine and interacts therewith, thus forming a common control apparatus.

It is known the quality of coffee-based drinks is strongly affected by brewing time and it is also known to adjust said brewing time in order to obtain a drink having optimum organoleptic properties.

More particularly, coffee machines are known in which the brewing time is measured and compared with a reference value: if the measured value does not fall within a tolerance range around the reference value, the brewing time is adjusted by modifying the coarseness of the coffee powder fed to the brewing arrangement.

To this purpose, coffee grinders are known in which the distance between the elements of the grinding members is adjustable, so that said elements can be brought closer or moved away relative to each other as needed: by adjusting the coarseness of the coffee powder it is possible to vary the brewing time and—accordingly—the organoleptic properties of the prepared drink until an optimum result is achieved.

The invention allows to obtain an improved adjustment with respect to the above-disclosed known coffee machines as it allows to create a correlation between the adjustment of the coarseness of ground coffee and brewing time and the adjustment of grinding time and weight of the ground coffee dose, which correlation was missing so far.

In fact, it is evident that in an optimized adjusting strategy, the coarseness of coffee powder affects the weight of the dose of such coffee powder for the preparation of a drink: a finer grinding leads to a lower weight, and vice versa.

In FIG. 7 a block diagram is illustrated which shows the operation of the coffee machine 101 and underlines the above correlation:

-   -   upon selection of a given coffee-based drink by the user, the         control device starts the preparation cycle;     -   the control device selects the corresponding value of ground         coffee coarseness stored therein and the corresponding value of         grinding time stored therein and sends corresponding signals to         the coffee grinder;     -   upon receiving said signals, the coffee grinder is started, the         distance between the elements of the grinding members of the         grinding chamber is set and the grinding members are activated         for grinding coffee for a time interval corresponding to the         grinding time received from the control device;     -   when said grinding time has lapsed, the grinding members of the         coffee grinder are stopped and the ground coffee is transferred         from the weighing assembly of the coffee grinder to the brewing         arrangement of the coffee machine;     -   the measured value of the ground coffee weight obtained by said         weighing assembly is sent to the control device and there it is         compared with a reference value corresponding to the         coffee-based drink and stored in said control device; if the         value measured by the weighing assembly is equal to the stored         reference value or falls within a tolerance range around said         reference value, no further action is taken; on the contrary, if         the value measured by the weighing assembly does not fall within         said tolerance range, the control device—by means of an         algorithm contained therein—calculates a new grinding time         suitable for obtaining the desired weight of the coffee dose for         the selected drink and replaces the stored grinding time value         by this new value calculated through said algorithm;     -   by using the ground coffee transferred to the brewing         arrangement, the coffee-based drink is prepared by said brewing         arrangement and delivered to the user through the dispensing         arrangement of the coffee machine;     -   the brewing time is measured and the measured value of the         brewing time is sent to the control device and compared with a         reference value corresponding to the coffee-based drink and         stored in said control device; if the measured value is equal to         the stored reference value or falls within a tolerance range         around said reference value, no further action is taken; on the         contrary, if the measured value does not fall within said         tolerance range, the control device—by means of an algorithm         contained therein—calculates a new ground coffee coarseness         suitable for obtaining the desired brewing time for the selected         drink and replaces the stored ground coffee coarseness value by         this new value calculated through said algorithm;     -   if a new ground coffee coarseness is calculated, the control         device—by means of a further algorithm contained         therein—calculates a new reference value for the coffee dose         weight that takes into account the different coarseness and         replaces the stored reference value by the new calculated value;         it also correspondingly adjusts the grinding time according to         the new reference value for the weight of the coffee dose.

Therefore, in the method according to the invention, even if the weight of the coffee dose obtained by the coffee grinder and/or the brewing time are not consistent with the respective reference values, no adjustment is made to the coffee grinder. On the contrary, a different grinding time and/or a different ground coffee coarseness are set for the successive grinding cycles (for the same drink); this means that the new values of the grinding time and/or of the ground coffee coarseness are sent to the coffee grinder when the current grinding cycle is already finished and the coffee grinder is ready for the next grinding cycle.

In order to determine the acceptable tolerance range around the reference value of the brewing time, at the beginning of the coffee grinder operation a certain number of measured values (samples) are stored in the control device and checked for determining the aforesaid tolerance range. Successively, the ground coffee coarseness is changed if the measured brewing times falls out of said tolerance range.

The same applies to the ground coffee weight, as disclosed above.

Advantageously, according to a preferred embodiment of the invention, the adjustment of the grinding time and the adjustment of the ground coffee coarseness are not carried out independently from each other, but they take into account the existing correlations.

Nevertheless, in an alternative embodiment of the invention, the adjustment of the grinding time and the adjustment of the ground coffee coarseness could also be carried out independently from each other.

It will be evident from the above that the invention achieves the objects set-forth above, as it allows to improve the adjustment of a coffee grinder and of the coffee machine to which said coffee grinder is mounted or connected.

It will also be evident that the provided description of preferred embodiments of the invention should not be intended as limiting and several modifications and variants within the reach of the person skilled in the art can be conceived without departing from the scope defined by the appended claims. 

The invention claimed is:
 1. A coffee grinder capable of being mounted to or connected to a coffee machine, the coffee grinder comprising: a hopper containing coffee beans; a grinding chamber to which the coffee beans are transferred from the hopper and in which one or more grinding members are provided for grinding the coffee beans and producing ground coffee, the grinding chamber comprising an outlet spout for discharging the ground coffee; and a weighing assembly comprising a container dedicated to weighing the ground coffee and weighing means operatively connected to the container, the container being arranged for receiving the ground coffee to be weighed from the outlet spout of the grinding chamber; wherein the coffee grinder comprises or is connected to a control device such that the coffee grinder receives as an input from the control device a signal for starting a grinding operation and a predetermined grinding time and such that the weighing assembly sends to the control device a measured value of the ground coffee weight measured by the weighing means at the end of the predetermined grinding time.
 2. A method for the operation of a coffee grinder mounted to or connected to a coffee machine, the coffee grinder comprising: a hopper containing coffee beans; a grinding chamber to which the coffee beans are transferred from the hopper and in which one or more grinding members are provided for grinding the coffee beans and producing ground coffee, the grinding chamber comprising an outlet spout for discharging the ground coffee; and a weighing assembly comprising a container dedicated to weighing the ground coffee and weighing means operatively connected to the container, the container being arranged for receiving the ground coffee to be weighed from the outlet spout of the grinding chamber; the method comprising: a control device of the coffee grinder or coffee machine sends to the coffee grinder a signal for starting the coffee grinder as well as a desired grinding time value; upon receiving the signal, the coffee grinder is started and the grinding members of the grinding chamber are activated for grinding coffee for the desired grinding time; the ground coffee is transferred from the grinding chamber to the container of the weighing assembly and is weighed by the weighing means; once the desired grinding time has lapsed, the grinding members are stopped and the ground coffee is discharged from the container; the measured value of the ground coffee weight obtained by the weighing means is sent to the control device and compared with a corresponding reference value, wherein, if the value measured by the weighing means does not fall within a given tolerance range around the reference value, the control device, by means of an algorithm contained in the control device, calculates a new grinding time for obtaining the reference value of the ground coffee weight and replaces the stored value of grinding time by the new value calculated by using the algorithm.
 3. The method according to claim 2, further comprising preliminarily storing in the control device a plurality of measured values of ground coffee weight in the control device and determining the tolerance range around the reference value of the ground coffee weight on the basis of the plurality of measured values.
 4. A method for the operation of a coffee machine, the coffee machine comprising a brewing arrangement, a dispensing arrangement, a coffee grinder, and a weighing assembly for weighing ground coffee, the weighing assembly being mounted to or connected to the coffee grinder or the brewing arrangement of the coffee machine and comprising a container dedicated to weighing ground coffee and weighing means operatively connected to the container, the container being arranged for receiving ground coffee discharged from the coffee grinder for being weighed by the weighing assembly and transferred to the brewing arrangement of the coffee machine, wherein the coffee machine and the coffee grinder comprise a common control device, the method comprising: upon selection of a given coffee-based drink by a user, the control device starts a preparation cycle such that the control device selects a corresponding stored value of ground coffee coarseness and a corresponding stored value of grinding time and sends corresponding signals to the coffee grinder; the coffee grinder is started, a distance between elements of grinding members of the coffee grinder is set and the grinding members are activated for grinding coffee for a time interval equal to the grinding time; once the grinding time has lapsed, the grinding members of the coffee grinder are stopped and the ground coffee is transferred from the weighing assembly to the brewing arrangement of the coffee machine such that the coffee-based drink is prepared by the brewing arrangement and delivered to the user through the dispensing arrangement of the coffee machine; a measured value of the ground coffee weight is obtained by the weighing assembly before the ground coffee is transferred to the brewing arrangement and the measured value of the ground coffee weight is sent to the control device and compared with a reference value corresponding to the selected drink and stored in the control device; and a brewing time needed for preparing the drink is measured and the measured value of the brewing time is sent to the control device and compared with a reference value corresponding to the selected drink and stored in the control device; wherein, if the measured value of the ground coffee weight does not fall within a given tolerance range around the reference value of the ground coffee weight stored in the control device, the control device by means of an algorithm contained by the control device, calculates a new grinding time suitable for obtaining the reference value of the ground coffee weight and replaces the stored value of grinding time by the new value calculated by using the algorithm; and wherein, if the measured value of the brewing time does not fall within a given tolerance range around the reference value of the brewing time stored in the control device, the control device, by means of an algorithm contained by the control device, calculates a new ground coffee coarseness suitable for obtaining the reference value of the brewing time and replaces the stored value of ground coffee coarseness by the new value calculated by using the algorithm.
 5. The method according to claim 4, wherein, if the measured value of the brewing time does not fall within the given tolerance range around the reference value of the brewing time stored in the control device, the control device, by means of an algorithm contained by the control device, calculates the new ground coffee coarseness suitable for obtaining the reference value of the brewing time and replaces the stored value of ground coffee coarseness by the new value calculated by using the algorithm and further calculates, by means of a further algorithm contained by the control device, a new reference value of the ground coffee weight on the basis of the new value of ground coffee coarseness and replaces the stored reference value of the ground coffee weight by the new calculated value and it adjusts the stored value of the grinding time depending on the new reference value of the ground coffee weight.
 6. The method according to claim 4, further comprising preliminarily storing a plurality of measured values of ground coffee weight in the control device and determining the tolerance range around the reference value of the ground coffee weight on the basis of the plurality of measured values and preliminarily storing a plurality of measured values of brewing time in the control device and determining the tolerance range around the reference value of the brewing time on the basis of the plurality of measured values.
 7. A method for the operation of a coffee machine, the coffee machine comprising a brewing arrangement, a dispensing arrangement, a weighing assembly for weighing ground coffee, and a coffee grinder, the weighing assembly being mounted to or connected to the coffee grinder or the brewing arrangement and comprising a container dedicated to weighing ground coffee and weighing means operatively connected to the container such that ground coffee discharged from the coffee grinder is weighed by the weighing assembly before being transferred to the brewing arrangement of the coffee machine, wherein the coffee machine and the coffee grinder comprise separate, respective control devices, which are interconnected for forming a common control apparatus, the method comprising: upon selection of a given coffee-based drink by a user, one of the control devices starts a preparation cycle such that one of the control devices selects a corresponding stored value of ground coffee coarseness and a corresponding stored value of grinding time and sends corresponding signals to the coffee grinder; the coffee grinder is started, a distance between elements of grinding members of the coffee grinder is set and the grinding members are activated for grinding coffee for a time interval equal to the grinding time; once the grinding time has lapsed, the grinding members of the coffee grinder are stopped and the ground coffee is transferred via the weighing assembly to the brewing arrangement of the coffee machine such that the coffee-based drink is prepared by the brewing arrangement and delivered to the user through the dispensing arrangement of the coffee machine; a measured value of the ground coffee weight is obtained by the weighing assembly before the ground coffee is transferred to the brewing arrangement and is sent to one of the control devices and compared with a reference value corresponding to the selected drink and stored in one of the control devices; a brewing time needed for preparing the drink is measured and the measured value of the brewing time is sent to one of the control devices and compared with a reference value corresponding to the selected drink and stored in one of the control devices; wherein, if the measured value of the ground coffee weight does not fall within a given tolerance range around the reference value of the ground coffee weight stored in one of the control devices, one of the control devices, by means of an algorithm contained therein, calculates a new grinding time suitable for obtaining the reference value of the ground coffee weight and replaces the stored value of grinding time by the new value calculated by using the algorithm; and wherein, if the measured value of the brewing time does not fall within a given tolerance range around the reference value of the brewing time stored in one of the control devices, one of the control devices, by means of an algorithm contained therein, calculates a new ground coffee coarseness suitable for obtaining the reference value of the brewing time and replaces the stored value of ground coffee coarseness by the new value calculated by using the algorithm.
 8. The coffee grinder according to claim 1, wherein the weighing means comprises a weighing cell. 